1. Field of the Invention
The present invention relates to a liquid crystal display device for use in a video projector, and a projection TV incorporating same.
2. Description of the Prior Art
Conventionally, a projection TV, one type of video projector, uses three cathode ray tubes (hereinafter referred to as CRT) for color display in red, green, and blue (which three colors are hereinafter referred to as R.G.B). Individual CRT images projected on a screen are synthesized to give a color image. However, the use of CRT involves a limitation in itself because projection of CRT images on a screen does not always provide an image having high luminance and high resolution. Recently, therefore, it has been proposed to use a liquid crystal display device in place of CRT. For example, Japanese Patent Publication No. 60-3291/1985 discloses a video projector using a liquid crystal display device.
A projection TV using a typical conventional liquid crystal display device will be explained with reference to FIG. 1. Liquid crystal display devices 4-6 have their respective display regions provided on different substrates. A drive IC (not shown) for driving pixels in each display region is mounted on each of the substrates. Such liquid crystal device is disclosed in, for example, Japanese Patent Publication No. 60-220317/1985. A light beam from a light source 1 is divided into three by two half mirrors 3 and two mirrors 2 so as to be incident on the three liquid crystal devices 4-6. The display region of each liquid crystal device is controlled by the corresponding drive IC so that only the desired pixels transmit light. The light beams transmitted through the liquid crystal devices 4-6 are projected on a screen 10 by projection lenses 7-9 for R.G.B., to form an image thereon.
With such arrangement, however, there is a certain distance d.sub.1, between the adjacent liquid crystal display devices. One reason is that a space is required for mounting a driving IC on each liquid crystal display device and also for formation of wiring thereon. Another reason is that a space is required for parts for fixing each LCD device (not shown) and parts for angular position adjustment. Therefore, a certain space must be provided between the projection lenses, resulting in the presence of an angle shown by .theta..sub.1. This angle .theta..sub.1 is a cause of a visual field angle trouble such that an image displayed may be seen redish or bluish according to the angle of view. Further, adjustment of relative angular position in all directions is required with respect to the three liquid crystal display devices to prevent color shifting on the screen. Such adjustment work requires considerable time and labor, and a large number of adjustment mechanisms. This is a serious problem indeed from the standpoint of production efficiency.
In the production of liquid crystal display devices, usually a plurality of arrays, each including drive IC mounting portions 12, wiring elements (not shown) for connecting terminal electrodes (not shown) of drive ICs and signal lines in display regions 13, are formed on one glass substrate 11, as shown in FIG. 2. FIG. 2 is a plan view showing four arrays formed on one substrate. The substrate is cut into the arrays. Then, a counter electrode substrate and drive ICs are mounted on each array to complete a liquid crystal display device. However, in the case of a liquid crystal display device of the active matrix type, in which switching elements are formed for driving individual pixels, more than tens of thousands of switching elements, such as thin film transistors (hereinafter to be referred to as TFT) must be formed for each display region. It is extremely difficult to form all the TFT's in one display region in such a way that they are characteristically uniform and defect-free. As such, there is a strong demand that as many arrays as possible are formed in one substrate so that they can be selectively used. With the conventional liquid crystal display devices, however, formation of 4 arrays in one substrate is the maximum possible limit, in view of the fact that the drive IC mounting portions must be formed. The drive IC mounting portions and wiring are formed of one or two layers of thin films, and accordingly they can be very easily formed. Therefore, it is unreasonable to form TFTs of the display region, the formation of which involves a very complex process, and the drive IC mounting portions on a same substrate.
It has been said that the production cost of a projection lens is proportional to 4 power of its diameter. Therefore, it is desirable to reduce lens diameter as far as possible. However, while the display region may be made smaller to some extent, the size of the drive IC's to be mounted may remain unchanged. Therefore, the drive IC mounting portions occupy a relatively large area.
For these reasons, it is impracticable to increase the number of arrays to be formed in one array. Therefore, the cost of array production is high, and it is extremely difficult to form all the TFTs on one display region characteristically uniform and defect-free.